The present invention relates generally to the field of electronic circuits and more particularly to a charge pump circuit.
Charge pumps are used in electronic circuits to provide voltages other than those provided by the power supply. Commonly charge pumps circuits are used in memory devices such as dynamic random access memory (DRAM) devices or EEPROMs (Electronic Erasable Programmable Read Only Memories). EEPROMs require larger voltage swings to write or erase memory cells. Most charge pumps are not able to efficiently transfer all of the charge in one stage to another stage or an output. As a result, more charge pump stages are required to reach a certain voltage. The inefficient transfer of charge results in less output current for a given clock speed.
Thus there exists a need for a charge pump circuit that has a more efficient charge transfer.
A charge pump circuit that achieves these goals includes a first capacitor having an input coupled to a first signal. A second capacitor has an input coupled to a second signal. A first diode has an anode coupled to an output of the first capacitor and a cathode coupled to an output of the second capacitor. A second diode has an anode coupled to the output of the second capacitor and a cathode coupled to the output of the first capacitor. A controllable switch has a control input coupled to the output of the second capacitor and couples the output of the first capacitor to an output of the charge pump circuit. In one embodiment, the first and second diode are field effect transistors configured as diodes and the controllable switch is a field effect transistor. The invention has a transient voltage overshoot at the gate of the transistor that turns the transistor on hard, which results in efficient charge transfer out of the capacitor. The efficient transfer of charge allows the capacitor to be smaller than prior art devices.